Tag Archives: cool roofing

A Look at Cool Roof Options

All photos courtesy Viridian Systems

by Ron Utzler

Within the built environment there are many avenues to energy savings. The energy efficiency of a building is affected by everything from lighting and windows, to insulation and reflective roofing. This article focuses on low-slope roofing materials that represent reflective roofing options.

Reflective roofing is typically a method of using light-colored surfacing that reflects more of the sun’s heat than it absorbs. A reflective value is the portion of light reflected, measured from 0 to 1, with higher values representing cooler surfaces. These values are measured with sophisticated, calibrated equipment under controlled conditions.

Providing roofs with a reflective surface is not a new concept. For example, asphalt coatings with leafing aluminum pigment have always promoted the benefit of reducing interior temperatures while slowing the oxidation of the waterproofing membrane. This reduces the load of air-conditioning systems and improves the occupant’s comfort, while extending the service life of the roof membrane.

However, the term ‘cool roofing’ was more recently coined with the increased focus on the reduction of energy consumption. As with any movement, there are opportunities for entrepreneurs to provide support and related services. Everything from third-party testing laboratories to new programs for certification have been evolving.

There are federal

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agencies, for example, that have decided all roofing in certain regions must meet Energy Star’s cool roofing requirements. The U.S. Environmental Protection Agency (EPA) established the voluntary Energy Star program which requires a roofing membrane to have an initial reflectance of .65 and a three-year-aged reflectance of .50 to be considered Energy Star rated. So, design teams should consider available roofing options in compliance with cool roofing requirements.

Cool roof systems are beneficial in climates where a building’s interior requires more cooling days, as opposed to heating days. Whether the goal is to reduce energy cost or improve the environment, building owners and specifiers must make educated decisions about roofing needs. To still have a cool roof, they need to be familiar with the available options, along with advantages, disadvantages, and cautions. This article contains a general overview of the low-slope roof system categories that can be installed with at least the initial reflectance to be considered a cool roof.

A fully adhered modified-bitumen (mod-bit) membrane is being installed with hot asphalt. The worker at the left is ‘sugaring’ loose granules into the asphalt at seams to produce a uniform reflective finish.

A white polyvinyl chloride (PVC) single-ply membrane provides a highly reflective, cool roofing assembly.

Single-ply membrane systems
As the name indicates, single-ply membrane assemblies are synthetic sheets in various combinations of compounds with or without reinforcement options, and installed in a single layer held in place by mechanical fasteners, adhesives, or some form of ballast. Most, if not all, of these membranes are available in white, and will provide the reflectance required to be considered a cool roof. Naturally, to take advantage of this reflectance, the membrane will either be adhered or mechanically fastened. A ballasted system may still qualify as a cool roof, depending on the color of the ballast itself.

Advantages of this assembly include:

application of one membrane will generally result in lower material and labor cost;
these membranes are typically available in bright white and their smooth surface provide the highest level of reflectance;
non-ballasted applications result in a smooth surface generally easier to visibly locate leak sources caused by defects or damage; and
in many cases, these membranes are manufactured with a gloss finish or clear film to provide a surface that resists dirt pickup, providing a self-cleaning attribute that can help maintain higher reflectance over time.

A disadvantage of this roof type is a single layer of waterproofing is more vulnerable to physical damage, resulting in wet insulation and interior leaks, depending on the deck type. For example, a structural concrete deck can hold more water in the system above the deck before it builds up to a break in the deck, allowing water to leak into the building. Unfortunately, this can cause more insulation damage from a single puncture because the leaks may go undetected until water enters the building’s interior. Of course, this concern for an unknown leak is based on the deck type and therefore applies to all systems, once the membrane’s waterproof integrity is broken.

Additionally, the anticipated useful life of a single-ply membrane is generally considered less than multiple-ply assemblies. This is most often viewed as an attribute of the mass (thickness) of the waterproofing membrane, which decreases over time by oxidation.

The amount of traffic on the membrane surface will also add a wear factor. Strategically placed walk treads helps can help.

When specifying these systems, it is important to keep in mind the membranes can be extremely slippery when wet. Further, because they are white means rainwater, dew, frost, and snow will be slower to evaporate. If someone is required to spend any length of time on a white membrane on a sunny day, wearing sunglasses is important.

Design teams should also be aware some membranes may have a short history of service in their current formulation. If a formula is changed to address a newly discovered performance issue, the alteration could produce a completely different, unanticipated problem after real exposure.

The local conditions of a particular roof exposure must also be considered. For example, if the roof will be exposed to chemical fallout from a manufacturing process, the chemical content and concentrations involved must be determined, so a membrane with the best resistance to those exposures is specified. The membrane supplier should be able to provide a chemical resistance chart for its product.

The photos above show a completed built-up roofing (BUR) system and light-colored gravel assembly.

Modified bitumen membrane systems
The modified-bitumen (mod-bit) membrane systems include sheet membranes made with asphalt typically modified with rubber or plastic compounds and reinforced with either glass or polyester mats. Typically, the surface ply is manufactured with light-colored mineral granules embedded.

Historically, these granules typically provided an initial reflectance value of .25 to .27 on a scale of 0 to 1. However, as the drive for energy savings grew, manufacturers developed brighter granules, or other methods to increase the product’s reflectivity. Some of these methods include the embedment of other synthetic white chips, rather than granules, or factory-coating the sheet with a brighter white coating.These brighter versions have raised the reflectance values to .70 to .80.

Such systems emerged in the United States in the 1980s after years of use in Europe, and have grown in popularity. Originally, the asphalt-based systems seemed a natural progression for contractors who were used to installing hot-applied built-up roofing (BUR) systems. They have reached a level of development where they are dependable membranes that also provide redundancy of plies.

Advantages of the mod-bit membrane systems are that they are typically installed in hot asphalt, cold-applied adhesive, heat welding or self-adhered, providing various options for the project’s needs. For example, getting hot asphalt to the top of a high-rise building may not be practical, but pails of cold-applied adhesive can be delivered to the roof. Also, maintenance and minor repairs can generally be completed with readily available asphalt materials.

An important attribute to the surface’s performance, the granulated membrane refers to the quality of the granule embedment. This is a key standard of quality that will determine how long the membrane weathers and wears before the mineral granules are dislodged and accumulate in the gutters and drain sumps. Referring to ASTM D4977/6164, Standard Test Method for Granule Adhesion to Mineral-surfaced Roofing by Abrasion, granule loss should not be greater than 2 grams. This value is not always reported in manufacturer’s product data sheets, but it is still an important feature to compare during the membrane selection process.

The consistency in granule color is not always able to be maintained by manufacturers. Slight variations from one production lot to another can show up on the same roof, leading to an inconsistent appearance in a finished project.

Since these systems are typically adhered with asphalt adhesives, it depends on the applicator’s expertise to avoid the unsightly appearance due to tracking the adhesive onto the finished surface, or uncontrolled bleed-out of adhesive at membrane laps. While the embedding of extra granules in the bleed out during application and applying white coating to tracked adhesive is often effective in providing a good finished appearance, this author is a proponent of post-coating the completed installation.

Due to the inconsistent shades of white previously mentioned and application aesthetics, the added initial cost to the project for the application of a quality acrylic elastomeric coating system can provide both immediate, and long-term benefits. It gives the immediate benefit of uniform appearance and maximum reflectivity, with the long-term advantage of an extended service life of the membrane. Even if the owner elects not to periodically recoat the surface, the initial coating can provide an additional five or more years of service as a sacrificial surfacing in the roof’s lifecycle.

The wide variety of membrane reinforcements and coating compounds means determining the right membrane for the given conditions will need to be an important aspect of the specification process. Design teams should factor in the anticipated amount of foot traffic on the roof system and include walk treads as a design element.

This highly reflective fleece-backed PVC is being fully adhered over a multiple ply asphalt BUR and seams are heat welded with an automatic hot-air welder.

After coating a new modified-bitumen membrane with white elastomeric coating provides a dual purpose—it provides a clean, uniform Energy Star system and adds film thickness to extend the system’s service life.

Built-up roof systems
As the name implies, built-up roofing (BUR) systems are assembled on the roof using multiple plies of reinforcement built-up with bitumen interply adhesives. Traditionally, BUR systems are surfaced with a flood coat of bitumen into which gravel is imbedded. While BUR is the oldest system, with a history long-term performance, it has fallen into disfavor with the rise in popularity of reflective cool roof systems. However, there are bright white gravels available for surfacing enabling the traditional BUR to qualify for cool roof status.

There has also been a rise in popularity in what is referred to as a ‘hybrid’ system. This combines the redundancy of reinforcement plies of BUR with the white granule surfacing of a mod-bit cap sheet. Traditional BUR with gravel provides a time-proven, durable system with a long lifecycle. Further, the gravel surface and number of plies provide traffic and puncture resistance.

Some disadvantages to these systems can include objection to the odor of hot bitumen at the project site and the ensuing potential complaints from the building occupants. However, there are fume-recovery equipment options, and there are cold-applied adhesive systems available.

In some high wind regions, gravel roofs may be resisted due to potential of gravel becoming projectiles. While this is a real concern for single-ply ballasted (i.e. loose-laid) roofs, the smaller gravel used to surface BUR roofs is typically adhered.

BUR roofs with gravel will generally weigh more than other membrane types, so the decks should be verified as capable of bearing the weight. If using hot asphalt or even cold adhesives, the surroundings and building occupancy should be taken into account and require a fume recovery or afterburner kettles for hot asphalt. Additionally, air intake vents should be covered during application.

With an ambient temperature of 27.7 C (82 F), note the surface temperature difference between a black surface (A), a standard granule surfaced modified-bitumen (B), and a granule modified-bitumen with an elastomeric white coating surface (C).

SPF systems
Sprayed-in-place polyurethane foam (SPF) systems combine two chemical components—isocyanate and resin—through specialized spray equipment. As the resulting liquid is applied to a substrate, it will expand 20 to 30 times its volume to form insulating polyurethane foam. The foam is generally applied in multiple passes of the spray gun resulting in layering 12.7 to 38 mm (½ to 1 ½ in.) per pass (or ‘lift’). A good applicator can control the lifts and construct a uniform taper to drains for proper water drainage.

Applications of SPF need to be surfaced to protect it from ultraviolet (UV) degradation, and to provide waterproofing, along with protection from physical damage and fire resistance.

The most typical surfacing is white elastomeric coating. A foam application is considered monolithic, as opposed to individual rigid insulation boards. This would reduce stress on the waterproofing membrane which could occur at the joints of rigid insulation.

Sprayfoam applications are considered self-flashing since each pass can be completed with a continuous movement from horizontal to vertical substrate. This reduces the chances of detailing errors in critical areas of stress.

The expertise of the applicator is crucial to the success of SPF systems. For example, if the component mixing is off ratio, the resulting foam would have different performance properties pertaining to rigidity or softness. Weather conditions during application are also crucial because of the way these products react to moisture. This can affect the foam’s surface texture, making effective coating application more difficult.

Conclusion
As demonstrated here, there are numerous roof systems that can qualify for cool roof ratings. The building owner’s individual needs and conditions will affect how the best system is selected.

It is important to keep in mind that no matter which roof system is selected; it will not perform as expected unless there is a proper evaluation of needs versus options, along with the appropriate budget. Additionally, detailed specifications with project-specific predesigned details need to be included. Finally, the installation should be contracted to a qualified applicator having experience with the specified system.

Ron Utzler has been involved in the technical aspects of commercial roofing systems for 35 years. He is currently technical director at Viridian Systems in Tallmadge, Ohio. Utzler can be reached by email at ronutzler@live.com.

TPO on Top: Why the Roofing Material Continues to Shine

by Mike Mendoza

Thermoplastic polyolefin (TPO) is a relatively new material, but makes up one of the fastest-growing sectors of the commercial roofing industry. All images courtesy Firestone Building Products

As building codes and environmental trends continue to evolve, so too does the diversity of roofing material options. These factors, along with others, make construction specifiers’ roofing installation and selection prowess of utmost importance.

Among the available choices is thermoplastic polyolefin (TPO). Despite the fact this technology is fairly new in the scheme of roof materials, it makes up one of the fastest-growing sectors of the commercial roofing industry. That growth brings with it constant improvements to the chemical composition of the membrane to achieve greater durability and longevity.

Nevertheless, representatives for the Single Ply Roofing Industry (SPRI) still point to early 1990s TPO installations that continue to perform thanks to proper installation and maintenance. SPRI data indicates about 371.6 million m² (4 billion sf) of TPO was installed in North America between 2005 and 2010, with nearly the entirety still performing without issue.¹

“We at SPRI are confident TPO roofing systems will continue to provide quality and value for many years to come,” said the association’s technical director, Mike Ennis.

Indeed, a 2013 study that used ASTM D6878, Standard Specification for Thermoplastic Polyolefin-based Sheet Roofing (revised to address concerns of prolonged exposure in extreme heat climates) shows the material’s durability.²

“The heat aging exposure at (116 C [240 F]) was extended from 670 hours to 5400 hours (32 weeks),” the study states. “To meet these new requirements, it is critical for TPO roofing formulations to contain high-quality resins combined with tailored stabilization, flame retardants, and membrane design.”

Results showed TPO roofing membranes produced using the right polymer formation and stabilization can perform in some of the most extreme climate conditions: “Depending on the climate zone, 1.5-mm (60-mil) membranes may last up to 25 years or more.”

Beyond durability, TPO single-ply roofing membranes offer several other performance and installation advantages. These assemblies can provide resistance to ultraviolet (UV) rays, ozone, and chemical exposure. Further, the reflective surface meets the U.S. Environmental Protection Agency’s (EPA’s) Energy Star requirements, and is both recyclable and composed of recycled content.

Knowing the options
Settling on the ideal TPO roofing system relies on identifying and analyzing the characteristics surrounding climate and condition of a commercial building’s existing roof surface. Factors include:
● potential for tears and abrasions;
● area wind speeds;
● UV exposure; and
● various surfaces (e.g. vertical parapet walls) and slopes.

When it comes to color choice, white is among the most popular option for reasons discussed later in this article. However, it is not the sole TPO variety to consider, particularly if another hue better suits a rooftop. In addition to white, TPO membranes often come in gray and tan.

Since TPO membranes are installed fully-adhered, ballasted, or mechanically fastened, they work with a range of building envelope designs, offering architects flexibility. Architects most commonly select TPO roofing for flat or low-slope installations because of its cost-effectiveness, easy installation, and heat-welded seams that prevent moisture penetration.

Keeping cool
A specific driving factor for choosing TPO is within the realm of cool roofing. The Cool Roof Rating Council (CRRC) was created in 1998 to “develop accurate and credible methods for evaluating and labeling the solar reflectance and thermal emittance of roofing products,” according to the nonprofit organization’s history and bylaws. In the 15 years or so since, a lot of roofing products now come in what can be considered ‘cool’ varieties.³ Field-applied coatings, single-plies, tiles, and others fit this bill, which the council defines as a surface that reflects and emits the sun’s heat back into the sky rather than transferring it to a building.

A roof’s solar reflectivity and thermal emittance (the ability to release absorbed heat), are both measurable factors, according to the U.S. Green Building Council (USGBC). The Green Building Alliance, a chapter serving the Greater Pittsburgh, Laurel Highlands, and Northwest Pennsylvania branches, says as many as 90 percent of roofs in the United States are, “poorly designed and built with dark, non-reflective heat-absorbing materials,” causing rooftop temperatures to hover as many as 50 C (90 F) above that of the air.

The more reflective a TPO surface, the more likely it will comply with increasingly stringent building codes. Therefore, white TPO membranes—the most reflective—can be a suitable choice for those striving for maximum energy savings and environmental benefits.

The U.S. Department of Energy (DOE) touches on this concept in its 2010 study entitled, “Guidelines for Selecting Cool Roofs,” stating a conventional dark-colored surface reflects about 20 percent of incoming sunlight while a “cool” light-colored one (white being the lightest) reflects as much as 80 percent.⁴

EPA goes one step further in its “Reducing Urban Heat Islands: Compendium of Strategies” focusing on cool roofs. The report uses a diagram from the Lawrence Berkeley National Laboratory (LBNL) to compare the solar reflectance of black, metal, and white roofs.⁵

On a hot, sunny summer day, a black roof that reflects five percent of the sun’s energy and emits more than 90 percent of the heat it absorbs can reach 82 C (180 F). A metal roof will reflect most of the sun’s energy while releasing about a fourth of the heat it absorbs; it can warm to 70 C (160 F). A cool roof will reflect and emit the majority of the sun’s energy and reach a peak temperature of 48 C (120 F).

CRRC lists white, tan, and gray TPO roofs among its ‘environmentally friendly’ options, and white and tan are compliant with California’s Title 24 Energy Efficiency Building Standards. Cool roof requirements have been adopted in several U.S. building energy codes, and an increasing percentage of electric utilities have begun offering rebates for cool roofing materials, including TPO, that help conserve energy and reduce buildings’ environmental impacts.

According to USGBC, TPO and other cool roof options yield the following benefits:
● utility rebate opportunities;
● lower indoor temperatures;
● reduced maintenance costs (partially due to the material’s longer lifespans);
● improved air quality resulting from a reduction of emissions such as mono-nitrogen oxides and carbon dioxides in the atmosphere;
● mitigated heat island indexes (i.e. less heat creation in dense, urban areas); and
● reduced energy bills because less air-conditioning is needed during the summer.

Conclusion
Not unlike other roofing product manufacturers, those offering TPO will recommend consulting a design professional to ensure proper roofing system selection, conformance to building codes, and insurance requirements. Such customizations further emphasize evaluating a roof’s current condition is paramount when determining how best to repair or replace it. Further with ever-changing code and material options available, it is important for construction professionals to remain educated about the changing commercial building products landscape.

Of course, amidst the increasingly popular cool roofing and TPO possibilities, it is crucial to be cognizant of the fact roofing materials are not the sole remedy to increase overall building performance. It takes a holistic approach to have a building perform at peak efficiency.

This fact emphasizes the importance of building products manufacturers working closely with architects and construction specifiers—as well as consultants, contractors, facility operators, and building owners—who share similar goals of increasing overall building performance.

Together, these professionals should consider the entire building envelope to continue revolutionizing the commercial building industry, yielding an impact that reaches far beyond their individual buildings, cities, and immediate populations.

Notes
¹ Visit www.spri.org/pdf/spri_responds_to_pro_roofing_article_on_tpo.pdf. (back to article)
² Visit msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_08e0/0901b803808e057f.pdf. (back to article )
³ See the council’s “Reducing Urban Heat Islands: Compendium of Strategies” by visiting www.epa.gov/hiri/resources/pdf/CoolRoofsCompendium.pdf. (back to article )
⁴ The DOE study can be found at www1.eere.energy.gov/femp/pdfs/coolroofguide.pdf. (back to article )
⁵ See S.L. Konopacki et al’s 1998 report, “Demonstration of Energy Savings of Cool Roofs,” also known as LBNL-40673. (back to article )

Mike Mendoza is the thermoplastic polyolefin (TPO) product manager for Firestone Building Products. He is responsible for researching market trends and directing the planning and development of thermoplastic products. Mendoza previously spent 13 years at Owens Corning where he served in various roles including as a southwest region sales manager for roofing, strategic product planning manager for asphalt, and director of global sourcing for insulation. He can be reached at mendozamichael@fsdp.com.